Reef-building shellfish such as mussels and oysters are particularly important on intertidal flats, where they facilitate many species by creating complex and solid structures in an otherwise sandy environment. In the Wadden Sea, intertidal mussel beds have dramatically decreased at the end of the 1980’s, and at present, these beds have only partly recovered. In this thesis, I have investigated the processes that limit the restoration of this important habitat, and more generally the mechanisms that underlie the persistence of natural intertidal mussel beds in the Wadden Sea.

My thesis highlights the importance of behavioural and morphological adaptation of mussels for their persistence in the dynamic intertidal environment. First, intertidal mussels proved better adapted to their wave-swept environment than transplanted subtidal mussels, limiting the persistence of the latter on intertidal flats. Second, movement adaptations proved an essential mechanism for forming spatial patterns in mussel beds, which in turn proved crucial for survival. Restoration techniques that aim to restore mussel beds should take into account how mussels adapt to their environment, but also adapt their environment to their needs, when attempting to restore the mussel beds to their former presence can be successful.